使用Java下载大文件

---

title: 使用Java下载大文件
date: 2017-09-04 04:51:12
tags: [Java]

主要思路是将大文件分解成若干个小文件进行下载.

本功能由两个类实现:DownLoadManager和DownloadThreadTask实现. 其中DownLoadManager类主要负责下载任务的初始化和调度, DownloadThreadTask主要负责处理下载任务.

用到的主要工具类有

1. org.apache.http.impl.client.CloseableHttpClient 模拟httpClient客户端发送http请求，可以控制到请求文件的字节位置。

2. BufferedInputStream都熟悉，用它接受请求来的流信息缓存。

3. RandomAccessFile文件随机类，可以向文件写入指定位置的流信息。

代码如下:

DownLoadManager

package util;

import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

import org.apache.commons.lang.exception.ExceptionUtils;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.impl.conn.PoolingHttpClientConnectionManager;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
 * 文件下载管理类
 */
public class DownLoadManager{
	private static final Logger LOGGER = LoggerFactory.getLogger(DownLoadManager.class);
	/**
	 * 每个线程下载的字节数
	 */
	private long unitSize = 1000 * 1024;
	private ExecutorService taskExecutor = Executors.newFixedThreadPool(10);
	
	private CloseableHttpClient httpClient;

	public DownLoadManager() {
		PoolingHttpClientConnectionManager cm = new PoolingHttpClientConnectionManager();
		cm.setMaxTotal(100);
		httpClient = HttpClients.custom().setConnectionManager(cm).build();
	}
	public static void main(String[] args) throws IOException {
		new DownLoadManager().doDownload();
	}
	/**
	 * 启动多个线程下载文件
	 */
	public void doDownload() throws IOException {
		//要下载的url
		String remoteFileUrl = "http://cn-sdjn-cu-v-04.acgvideo.com/vg4/e/60/21029304-1.mp4?expires=1504513500&platform=pc&ssig=4-pYfuQHUKppz3XGrw6Hnw&oi=1032322900&nfa=T7l/1XWXSxfil4KoioiGpQ==&dynamic=1&hfa=2073962963&hfb=Yjk5ZmZjM2M1YzY4ZjAwYTMzMTIzYmIyNWY4ODJkNWI=";
		String localPath = "E://temp//";
		String fileName = new URL(remoteFileUrl).getFile();
		System.out.println("远程文件名称：" + fileName);
		fileName = fileName.substring(fileName.lastIndexOf("/") + 1, fileName.length()).replace("%20", " ");

		System.out.println("本地文件名称：" + fileName);
		long fileSize = this.getRemoteFileSize(remoteFileUrl);
		this.createFile(localPath + System.currentTimeMillis() + fileName, fileSize);
		Long threadCount = (fileSize / unitSize) + (fileSize % unitSize != 0 ? 1 : 0);
		long offset = 0;
		
		CountDownLatch end = new CountDownLatch(threadCount.intValue());
		if (fileSize <= unitSize) {// 如果远程文件尺寸小于等于unitSize
			DownloadThreadTask downloadThread = new DownloadThreadTask(remoteFileUrl, localPath + fileName, offset, fileSize, end, httpClient);
			taskExecutor.execute(downloadThread);
		} else {// 如果远程文件尺寸大于unitSize
			for (int i = 1; i < threadCount; i++) {
				DownloadThreadTask downloadThread = new DownloadThreadTask(remoteFileUrl, localPath + fileName, offset, unitSize, end, httpClient);
				taskExecutor.execute(downloadThread);
				offset = offset + unitSize;
			}
			if (fileSize % unitSize != 0) {// 如果不能整除，则需要再创建一个线程下载剩余字节
				DownloadThreadTask downloadThread = new DownloadThreadTask(remoteFileUrl, localPath + fileName, offset, fileSize - unitSize * (threadCount - 1), end, httpClient);
				taskExecutor.execute(downloadThread);
			}
		}
		try {
			end.await();
		} catch (InterruptedException e) {
			LOGGER.error("DownLoadManager exception msg:{}", ExceptionUtils.getFullStackTrace(e));
			e.printStackTrace();
		}
		taskExecutor.shutdown();
		LOGGER.debug("下载完成！{} ", localPath + fileName);
	}

	/**
	 * 获取远程文件尺寸
	 */
	private long getRemoteFileSize(String remoteFileUrl) throws IOException {
		long fileSize = 0;
		HttpURLConnection httpConnection = (HttpURLConnection) new URL(remoteFileUrl).openConnection();
		//使用HEAD方法
		httpConnection.setRequestMethod("HEAD");
		int responseCode = httpConnection.getResponseCode();
		if (responseCode >= 400) {
			LOGGER.debug("Web服务器响应错误!");
			return 0;
		}
		String sHeader;
		for (int i = 1;; i++) {
			sHeader = httpConnection.getHeaderFieldKey(i);
			if (sHeader != null && sHeader.equals("Content-Length")) {
				System.out.println("文件大小ContentLength:" + httpConnection.getContentLength());
				fileSize = Long.parseLong(httpConnection.getHeaderField(sHeader));
				break;
			}
		}
		return fileSize;
	}

	/**
	 * 创建指定大小的文件
	 */
	private void createFile(String fileName, long fileSize) throws IOException {
		File newFile = new File(fileName);
		RandomAccessFile raf = new RandomAccessFile(newFile, "rw");
		raf.setLength(fileSize);
		raf.close();
	}
}

DownloadThreadTask

package util;

import java.io.BufferedInputStream;
import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.util.concurrent.CountDownLatch;
import org.apache.commons.lang.exception.ExceptionUtils;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.protocol.BasicHttpContext;
import org.apache.http.protocol.HttpContext;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * 负责文件下载的类
 */
public class DownloadThreadTask implements Runnable {

	private static final Logger LOGGER = LoggerFactory.getLogger(DownloadThreadTask.class);

	/**
	 * 待下载的文件
	 */
	private String url = null;

	/**
	 * 本地文件名
	 */
	private String fileName = null;

	/**
	 * 偏移量
	 */
	private long offset = 0;

	/**
	 * 分配给本线程的下载字节数
	 */
	private long length = 0;
	
	private CountDownLatch end;
	private CloseableHttpClient httpClient;
	private HttpContext context;

	/**
	 * @param url
	 *            下载文件地址
	 * @param fileName
	 *            另存文件名
	 * @param offset
	 *            本线程下载偏移量
	 * @param length
	 *            本线程下载长度
	 */
	public DownloadThreadTask(String url, String file, long offset, long length, CountDownLatch end, CloseableHttpClient httpClient) {
		this.url = url;
		this.fileName = file;
		this.offset = offset;
		this.length = length;
		this.end = end;
		this.httpClient = httpClient;
		this.context = new BasicHttpContext();
		LOGGER.debug("偏移量=" + offset + ";字节数=" + length);
	}
	
	public void run() {
		try {
			HttpGet httpGet = new HttpGet(this.url);
			httpGet.addHeader("Range", "bytes=" + this.offset + "-" + (this.offset + this.length - 1));
			httpGet.addHeader("Referer", "http://api.bilibili.com");
			CloseableHttpResponse response = httpClient.execute(httpGet, context);
			BufferedInputStream bis = new BufferedInputStream(response.getEntity().getContent());
			byte[] buff = new byte[1024];
			int bytesRead;
			File newFile = new File(fileName);
			RandomAccessFile raf = new RandomAccessFile(newFile, "rw");
			while ((bytesRead = bis.read(buff, 0, buff.length)) != -1) {
				raf.seek(this.offset);
				raf.write(buff, 0, bytesRead);
				this.offset = this.offset + bytesRead;
			}
			raf.close();
			bis.close();
		} catch (ClientProtocolException e) {
			LOGGER.error("DownloadThread exception msg:{}", ExceptionUtils.getFullStackTrace(e));
		} catch (IOException e) {
			LOGGER.error("DownloadThread exception msg:{}", ExceptionUtils.getFullStackTrace(e));
		} finally {
			end.countDown();
			LOGGER.info(end.getCount() + " is go on!");
			System.out.println(end.getCount() + " is go on!");
		}
	}
}